Apparatus for and method of electro-optically reading a target in the presence of ambient light by detecting and suppressing the ambient light

ABSTRACT

A target is read in the presence of ambient light. A scan component scans a laser beam across the target. A detector assembly detects and converts return laser light from the target into an information signal bearing information related to the target, and concomitantly detects and converts the ambient light into an ambient light signal. The assembly includes a first photodetector for generating a first output signal comprised of the information and the ambient light signals, a detector lens for focusing and directing the return laser light substantially onto the first photodetector, and a second photodetector for generating a second output signal substantially comprised of the ambient light signal. Signal processing circuitry processes the output signals to determine a magnitude of the ambient light signal, and suppresses the ambient light signal when the determined magnitude of the ambient light signal at least equals a threshold.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to an apparatus for, and amethod of, electro-optically reading a target in the presence of ambientlight and, more particularly, to detecting and suppressing the ambientlight, especially when emitted from fluorescent lamps and light emittingdiodes (LEDs) operated at kilohertz frequencies.

BACKGROUND

Moving laser beam readers or laser scanners have long been used as datacapture devices to electro-optically read targets, such asone-dimensional bar code symbols, particularly of the Universal ProductCode (UPC) type, printed on labels associated with products in manyvenues, such as supermarkets, warehouse clubs, department stores, andother kinds of retailers, as well as many other venues, such aslibraries and factories. The moving laser beam reader generally includesa housing, a laser for emitting a laser beam, a focusing lens assemblyfor focusing the laser beam to form a beam spot having a certain size ata focal plane in a range of working distances relative to the housing, ascan component for repetitively scanning the beam spot across a targetin a scan pattern, for example, a scan line or a series of scan lines,across the target multiple times per second, and a photodetector fordetecting return laser light reflected and/or scattered from the targetand for converting the detected return laser light into an output analogelectrical information signal bearing information related to the target.This analog electrical information signal varies in amplitude as afunction of time due to the time-varying return laser light along eachscan line, and varies in frequency as a function of the density of thesymbol, as well as the distance at which the symbol is being read. Themoving laser beam reader also includes signal processing receivercircuitry including a digitizer for digitizing the variable analoginformation signal, and a microprocessor for decoding the digitizedsignal based upon a specific symbology used for the target. The decodedsignal identifies the product and is transmitted to a host, e.g., a cashregister in a retail venue, for further processing, e.g., product pricelook-up or product inventorying.

In one advantageous embodiment, during operation of the moving laserbeam reader in a venue having one or more external light sources thatemit ambient light, an operator holds the housing in his or her hand,and aims the housing at the target, and then initiates the data captureand the reading of the target by manual actuation of a trigger on thehousing. The ambient light is also concomitantly detected by thephotodetector, which generates an analog electrical ambient lightsignal. In the event that the external source is sunlight, then theambient light is substantially constant in magnitude, and therefore, theanalog electrical ambient light signal has a constant illumination DCcomponent. In the event that the external source is an incandescent bulbor a fluorescent lamp energized at 50 Hz or 60 Hz, then the analogelectrical ambient light signal has a constant illumination DC componentand a relatively small time-varying AC frequency component at 50 Hz or60 Hz. In the event that the fluorescent lamp is operated at higherfrequencies for greater luminous efficiency, or in the event that theexternal source includes light emitting diodes (LEDs) operated at higherfrequencies, then the analog electrical ambient light signal has aconstant illumination DC component and a relatively larger time-varyingAC frequency component at kilohertz frequencies, typically anywhere from30 kHz to 300 kHz.

In some circumstances, the presence of the ambient light signalinterferes with, and weakens, the information signal. To prevent suchinterference, the constant illumination DC component of the ambientlight signal can generally be filtered out from the information signal.Also, filters can be used to suppress the ambient light signal when itstime-varying frequency component is very far in frequency away from thefrequency of the information signal. However, if the time-varyingfrequency component of the ambient light signal is too close infrequency to the frequency of the information signal, then the ambientlight signal can interfere and impede the decoding of the informationsignal, thus degrading the performance of the reader. By way ofnon-limiting example, an information signal of about 50 kHz can begenerated during reading of a low density symbol located relativelyclose to the reader, e.g., about 10 inches away. If the ambient lightsource includes LEDs operated at about 50 kHz, then the respectivefrequencies of the ambient light signal and the information signal aretoo close and will cause an interference, and perhaps cause the symbolnot to be successfully decoded and read.

To prevent such interference, it is also known to reduce the ambientlight signal by placing a detector lens in front of the photodetector.The detector lens can be implemented either as a transmissive or areflective component. The detector lens limits the field of view (FOV)of the photodetector. The FOV is minimized and limited to desirablyinclude substantially only the laser beam spot. Still, even within thislimited FOV, the ambient light signal can still be too high forsuccessful decoding.

To detect and measure the magnitude of the ambient light signal, it isknown to analyze an output analog electrical signal of the photodetectorwhen the laser is deenergized, i.e., when there is no informationsignal. This typically occurs at the start of a reading session, e.g.,during a start of scan (SOS) frame, which, for example, advantageouslylasts for about 16 milliseconds. When the laser is deenergized, however,the target cannot be read, and the reader must wait for the laser to beenergized. If the ambient light signal is, for some reason, not detectedduring this initial deenergization of the laser, then the reader mustwait for the next time that the laser is deenergized to attempt thedetection of the ambient light signal again. All this waiting negativelyimpacts the reader's aggressiveness and renders its performancesluggish.

Accordingly, there is a need to suppress such interference caused bysuch ambient light and to enhance reader performance without having todeenergize the laser.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, together with the detailed description below, are incorporated inand foini part of the specification, and serve to further illustrateembodiments of concepts that include the claimed invention, and explainvarious principles and advantages of those embodiments.

FIG. 1 is a schematic view of a handheld moving laser beam readerapparatus operative for detecting and suppressing an ambient lightsignal in accordance with the present disclosure.

FIG. 2 is an electrical circuit schematic of one embodiment of a signalprocessing receiver circuit in one mode of operation for use in theapparatus of FIG. 1.

FIG. 3 is analogous to FIG. 2, but in another mode of operation.

FIG. 4 is an electrical circuit schematic of part of another embodimentof a signal processing receiver circuit for use in the apparatus of FIG.1.

FIG. 5 is a front view of a set of photodetectors of a detector assemblyemployed in the circuit of FIGS. 2-4.

FIG. 6 is a front view of the set of photodetectors of FIG. 5 depictingreturn laser light thereon from a target, as well as ambient light.

FIG. 7 is a diagram of light rays passing through a detector lens to theset of photodetectors of FIG. 5.

FIG. 8 is a flow chart depicting steps performed in accordance with themethod of the present disclosure.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions and locations of some of theelements in the figures may be exaggerated relative to other elements tohelp to improve understanding of embodiments of the present invention.

The apparatus and method components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present invention so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

DETAILED DESCRIPTION

One aspect of this disclosure relates to an apparatus or reader forelectro-optically reading a target, e.g., a bar code symbol, in thepresence of ambient light to be suppressed. The reader includes a laser,typically a semiconductor laser diode, for emitting a laser beam. Thereader also includes a scan component for scanning the laser beam acrossthe target for reflection and scattering therefrom as return laserlight. The reader also includes a detector assembly for detecting thereturn laser light from the target and for converting the detectedreturn laser light into an analog electrical information signal bearinginformation related to the target, and for concomitantly detecting theambient light and for converting the detected ambient light into ananalog electrical ambient light signal. The detector assembly includes afirst photodetector having a first field of view and a first lightcollection area, a second photodetector having a second field of viewand a second light collection area in close proximity to the first lightcollection area, and a detector lens spaced from the first and secondphotodetectors and operative for focusing and directing the return laserlight substantially onto the first light collection area over the firstfield of view. The first light collection area is operative forgenerating a first analog electrical output signal comprised of theinformation signal and the ambient light signal, and the second lightcollection area is operative for generating a second analog electricaloutput signal substantially comprised of the ambient light signal. Thereader further includes signal processing circuitry for processing thefirst and second output signals to determine a magnitude of the ambientlight signal, and for suppressing the ambient light signal when thedetermined magnitude of the ambient light signal at least equals, andpreferably, exceeds, a threshold.

More particularly, the signal processing circuitry includes acontroller, e.g., a programmed microprocessor, for comparing the ambientlight signal from the second photodetector with the threshold. Thesignal processing circuitry is operative for processing the first outputsignal in one mode of operation when the ambient light signal from thesecond photodetector is below the threshold, and for suppressing theambient light signal in the first output signal and for processingsubstantially only the information signal in the first output signal inanother mode of operation when the ambient light signal from the secondphotodetector at least equals the threshold.

In one embodiment, the signal processing circuitry includes a correlateddouble sampling (CDS) circuit for suppressing the ambient light signalin the first output signal, and a control switch having two switchingstates. The controller is operative for switching the control switch toone of the switching states in which the CDS circuit is bypassed duringthe one mode of operation, and for switching the control switch to theother of the switching states in which both the information signal andthe ambient light signal in the first output signal are conducted to theCDS circuit during the other mode of operation.

In another embodiment, the signal processing circuitry includes abandpass filter for suppressing the ambient light signal in the firstoutput signal, and a control switch having two switching states. Thecontroller is operative for switching the control switch to one of theswitching states in which the bandpass filter is bypassed during the onemode of operation, and for switching the control switch to the other ofthe switching states in which both the information signal and theambient light signal in the first output signal are conducted to thebandpass filter during the other mode of operation.

Another aspect of this disclosure resides in the above-describeddetector assembly, which comprises a first photodetector having a firstfield of view and a first light collection area, a second photodetectorhaving a second field of view and a second light collection area inclose proximity to the first light collection area, and a detector lensspaced from the first and second photodetectors and operative forfocusing and directing the return laser light substantially onto thefirst light collection area over the first field of view. The firstlight collection area is operative for generating a first analogelectrical output signal comprised of the information signal and theambient light signal, and the second light collection area is operativefor generating a second analog electrical output signal substantiallycomprised of the ambient light signal. Preferably, each light collectionarea is elongated, and the light collection areas lie on a commonsubstrate. Advantageously, the second light collection area liesexteriorly of, and preferably, surrounds, the first light collectionarea.

A method, in accordance with still another aspect of this disclosure, ofelectro-optically reading a target in the presence of ambient light tobe suppressed, is performed by emitting a laser beam; by scanning thelaser beam across the target for reflection and scattering therefrom asreturn laser light; by detecting the return laser light from the target;by converting the detected return laser light into an analog electricalinformation signal bearing information related to the target; byconcomitantly detecting the ambient light; by converting the detectedambient light into an analog electrical ambient light signal; bygenerating a first analog electrical output signal comprised of theinformation signal and the ambient light signal from a firstphotodetector having a first field of view and a first light collectionarea; by generating a second analog electrical output signalsubstantially comprised of the ambient light signal from a secondphotodetector having a second field of view and a second lightcollection area in close proximity to the first light collection area;by focusing and directing the return laser light substantially onto thefirst light collection area over the first field of view; by processingthe first and second output signals to determine a magnitude of theambient light signal; and by suppressing the ambient light signal whenthe determined magnitude of the ambient light signal at least equals athreshold.

Turning now to the drawings, FIG. 1 depicts a handheld, moving laserbeam reader 10 implemented in a gun-shaped housing 55 having apistol-grip type of handle 53. The housing 55 contains a laser lightsource 46, preferably a semiconductor laser diode, for emitting anoutgoing laser beam 51 to a target, such as a bar code symbol 70, forreflection and scattering therefrom; a detector assembly 58, preferablya pair of photodiodes PD1 and PD2, and a detector lens L, as describedmore fully below in connection with FIGS. 5-7, for detecting incominglight 52; a focusing optical assembly 57, preferably one or morefocusing lenses, for focusing the outgoing laser beam 51 as a laser beamspot on the symbol 70; an application specific integrated circuit (ASIC)20 mounted on a printed circuit board (PCB) 61; a programmedmicroprocessor or controller 40, also preferably mounted on the PCB 61;and a power source or battery 62, preferably mounted in the handle 53. Alight-transmissive window 56 at a front end of the housing 55 allows theoutgoing laser light beam 51 to exit the housing 55, and the incominglight 52 to enter the housing 55. A user holds the reader 10 by thehandle 53, and aims the reader 10 at the symbol 70, preferably at adistance away from the symbol 70. To initiate reading, the user pulls atrigger 54 on the handle 53. The reader 10 may optionally include akeyboard 48 and a display 49 readily accessible to the user.

As further depicted in FIG. 1, the outgoing laser beam 51 emitted by thelaser light source 46 passes through a partially-silvered mirror 47 to ascan component or oscillating scan mirror 59, which is coupled to adrive motor 60, preferably energized when the trigger 54 is manuallypulled. The oscillation of the mirror 59 causes the outgoing laser beam51 to sweep back and forth in a desired scan pattern, e.g., a scan line,across the symbol 70. A variety of mirror and motor configurations canbe used to move the laser beam in the desired scan pattern. For example,the mirror 59 need not be a concave mirror as illustrated, but could bea planar mirror that is repetitively and reciprocally driven inalternate circumferential directions about a drive shaft on which theplanar mirror is mounted.

As further depicted in FIG. 1, the incoming light 52 may have two lightcomponents that come from two different sources. The first lightcomponent is return laser light derived from the laser light source 46and is generated by reflection and/or scattering of the laser light beam51 back by the symbol 70 through the window 56. The second lightcomponent is ambient light 82 derived from an external ambient lightsource 80 operative for emitting the ambient light 82, which passesthrough the window 56. As described above, the external light source 80at a venue can be sunlight, one or more incandescent bulbs, one or morefluorescent lamps, one or more light emitting diodes (LEDs), and thelike. In the exemplary reader 10 shown in FIG. 1, the incoming light 52reflects off of the scan mirror 59 and the partially-silvered mirror 47and impinges on the detector assembly 58. The detector assembly 58produces an analog electrical output signal proportional to theintensity of the received return light 52. A first component signal ofthe output signal, which is produced from the return laser light derivedfrom the laser light source 46, is hereinafter described as an“information” signal (V_(ABP)) bearing information related to the symbol70. The subscript ABP is an abbreviation for analog bar pattern. Asecond component signal of the output signal, which is produced from theambient light derived from the ambient light source 80, is hereinafterdescribed as an “ambient light” signal (V_(AMP)).

As also described above, when fluorescent lamps and LEDs are operated atkilohertz frequencies, there are circumstances where the time-varyingfrequency component of the ambient light signal V_(AMB) is too close infrequency to the frequency of the information signal V_(ABP), in whichevent the ambient light signal V_(AMB) can interfere and impede thedecoding of the information signal V_(ABP), thus degrading theperformance of the reader 10. By way of non-limiting example, aninformation signal V_(ABP) of about 50 kHz can be generated duringreading of a low density symbol 70 located relatively close to thereader 10, e.g., about 10 inches away. If the LEDs are operated at about50 kHz, then the respective frequencies of the ambient light signalV_(AMB) and the information signal V_(ABP) are too close and will causean interference, and perhaps cause the symbol 70 not to be successfullyread. One aspect of this disclosure is to detect and suppress suchinterference, without denergizing the laser light source 46, and withoutnegatively impacting the reader's aggressiveness and without renderingits performance as sluggish.

In accordance with this disclosure, the detector assembly 58, as bestshown in FIGS. 5-7, includes a first photodetector PD1 having a firstfield of view (FOV1) and a first light collection area 12, a secondphotodetector PD2 having a second field of view (FOV2) and a secondlight collection area 14, and a detector lens L spaced from the firstand second photodetectors PD1, PD2 and operative for focusing anddirecting the return laser light substantially onto the first lightcollection area 12 over the first field of view FOV1. The first lightcollection area 12 is in close proximity to, or at least partly, and, asshown, may be entirely, surrounded by, the second collection area 14.The detector lens L may be a stand-alone component as shown in FIG. 7,or may be integrally implemented as curved surfaces of the mirrors 47and 59 of FIG. 1. The detector lens L optically modifies and configuresthe first field of view FOV1 and the second field of view FOV2. FOV1 maybe smaller than FOV2 as shown in FIG. 7, or FOV2 may be divided intosubfields, each of which is smaller than FOV1.

The first photodetector PD1 can thus, for example, be termed an interioror central photodetector, while the second photodetector PD2 can betermed an exterior photodetector. The first and the second collectionareas 12, 14 are generally planar and are situated, typically bywafer-scale processing, on a common, generally planar substrate 90,preferably made of silicon. The first and the second light collectionareas 12, 14 have centers with optical axes that pass therethrough andthat are generally perpendicular to the substrate 90. These optical axesare substantially collinear, or are parallel to each other. Although PD1and PD2 have been illustrated with light collection areas 12, 14 thatare shaped as rectangles, it will be understood that many other shapes,e.g., ovals, may be used. Although the first light collection area 12 ofPD1 has been illustrated as being centrally and symmetrically locatedwithin the second light collection area 14 of PD2, it will be understoodthat this need not be; for example, the first light collection area 12can be offset from, or shifted to an asymmetrical position relative to,the second light collection area 14 such that the second lightcollection area 14 bounds the first light collection area 12 on onlythree of its four sides.

As shown in FIG. 6, each light collection area 12, 14 receives thereturn laser light derived from the laser light source 46, and receivesthe ambient light from the ambient light source 80, but to differentextents, as described below. Each light collection area 12, 14 convertsthe received return laser light derived from the laser light source 46into the information signal V_(ABP), and also converts the receivedambient light from the ambient light source 80 into the ambient lightsignal V_(AMB).

The first light collection area 12 of PD1 generates a first analogelectrical output signal comprised of the information signal V_(ABP) andthe ambient light signal V_(AMB) for both close-in and far-out targets,while the second light collection area 14 of PD2 generates a secondanalog electrical output signal substantially comprised of the ambientlight signal V_(ABP), especially for far-out targets, because the returnlaser light derived from the laser light source 46 is focused by thedetector lens L onto the first light collection area 12 of PD1. Hence,as described below, the second light collection area 14 of PD2 may beemployed to detect the ambient light signal V_(AMB). It is not necessaryto deenergize the laser light source 46 in order for the second lightcollection area 14 of PD2 to detect the ambient light signal V_(AMB).

The ASIC 20, as shown in the embodiment of FIGS. 2-3, includes a signalprocessing receiver circuit having a first channel connected to thefirst photodetector PD1, and a second channel connected to the secondphotodetector PD2. As described above, the first photodetector PD1outputs a combined or composite output signal (V_(ABP)+V_(AMB)) that isthe sum of the information signal V_(ABP) and the ambient light signalV_(AMB). The first channel of the signal processing receiver circuitincludes a front-end receiver section 100 having at least one amplifier(AMP1), advantageously configured as a transimpedance amplifier, toincrease the gain of the analog electrical combined output signal(V_(ABP)+V_(AMB)) received from the first photodetector PD1. The gain ofthe amplifier AMP1 can be adjusted by varying a resistor 102 via acontrol line 104 connected to the controller 40. The combined outputsignal (V_(ABP)+V_(AMB)) is either directly conducted to a back-endreceiver section 120 in a first mode of operation by having thecontroller 40 switch a bypass switch S3 via a control line 106 to afirst switching state as depicted in FIG. 2, or is directly connected toan ambient light suppression circuit 140 in a second mode of operationby having the controller 40 switch the bypass switch S3 via the controlline 106 to a second switching state as depicted in FIG. 3.

The switching of the bypass switch S3 is determined by the signalprocessing receiver circuit by measuring the ambient light signalV_(AMB) detected by the second photodetector PD2, as described below. Ifthe measured ambient light signal V_(AMB) is below a threshold value,then the presence of the ambient light signal V_(AMB) can be toleratedand, hence, the combined output signal (V_(ABP)+V_(AMB)) is sent to theback-end receiver section 120 in the first mode of operation depicted inFIG. 2. If the measured ambient light signal V_(AMB) equals or exceedsthe threshold value, then the presence of the ambient light signalV_(AMB) will interfere with the reading of the symbol 70 and, hence, theambient light signal V_(AMB) must be suppressed by the suppressioncircuit 140, and only the information signal V_(ABP) is sent to theback-end receiver section 120 in the second mode of operation depictedin FIG. 3. The threshold value can be stored in advance in a memory ofthe controller 40.

The controller 40 controls the laser light source 46 with a laser drivecircuit 108 via a control line 110. The laser drive circuit 108 includesa laser power regulator, which is a closed loop feedback system thatmaintains a constant optical output power by varying the applied forwardcontinuous current I_(C) (FIG. 2) or a modulated current I_(MOD) (FIG.3) to the laser light source 46. The laser light source 46 includes alaser diode 112 and a monitor photodiode 114. A small fraction of theoutput laser light is coupled into the monitor photodiode 114 within theenclosed laser light source 46. This induces a photocurrent in themonitor photodiode 114 that is proportional to the laser output power.This photocurrent is a negative feedback signal that is used to regulatethe laser's output power. Thus, the controller 40 can eithercontinuously run the laser light source 46 in a continuous mode, or canmodulate the laser light source 46 in a modulated mode.

Thus, in FIG. 2, the combined output signal (V_(ABP)+V_(AMB)) isconducted to the back-end receiver section 120, which includes anautomatic gain controller (AGC) having an on/off control, at least oneactive low-pass filter stage having an adjustable cutoff frequency inits bandwidth to filter noise from the combined output signal, and atleast one amplifier (AMP2) having an adjustable gain to increase thegain of the combined output signal. Each of the AGC, low-pass filter,and the AMP2 has a control input connected to control lines 116, 118,122, which can be adjusted under control of the microprocessor 40.

The signal processing receiver circuit also includes a digitizer 124which digitizes the combined output signal by processing the same withdifferentiating circuits, peak detectors, multiplexers, logic elements,and comparators. The digitizer 124 processes the combined output signalfrom the back-end section 120 to produce a pulse signal where the widthsand spacings between the pulses correspond to the widths of the bars andthe spacings between the bars of the symbol 70. The digitizer 124 servesas an edge detector or wave shaper circuit, and threshold points set bythe digitizer 124 determines what points of the combined output signalrepresent bar edges. The pulse signal from the digitizer 124 is appliedto a decoder 128, typically incorporated as software in the programmedcontroller 40, which will also have associated program memory and randomaccess data memory. The controller 40 also has an analog-to-digitalconverter (ADC) 126 connected to the decoder 128 and to the output ofthe back-end section 120. The decoder 128 first determines the pulsewidths and spacings of the combined output signal from the digitizer124. The decoder 128 then analyzes the widths and spacings to find anddecode a legitimate bar code symbol. This includes analysis to recognizelegitimate characters and sequences, as defined by the appropriate codestandard. The controller 40 then communicates with an external host overan interface.

The measuring of a magnitude and/or a frequency of the ambient lightsignal V_(AMB) is performed by the second photodetector PD2 and thecontroller 40 in various ways. As described above, the secondphotodetector PD2 outputs an output signal that is substantiallycomprised of the ambient light signal V_(AMB). The second channel of thesignal processing receiver circuit includes at least one amplifier(AMP4) 22, advantageously configured as a transimpedance amplifier, toincrease the gain of the ambient light signal V_(AMB) received from thesecond photodetector PD2. The gain of the amplifier 22 can be adjustedby varying a resistor 24 via a control line 38 connected to thecontroller 40. The amplified ambient light signal V_(AMB) is conductedto an automatic gain controller (AGC) 26 having an on/off control, atleast one active low-pass filter stage 28 having an adjustable cutofffrequency in its bandwidth to filter noise from the amplified ambientlight signal V_(AMB), at least one amplifier (AMP5) 30 having anadjustable gain to increase the gain of the amplified ambient lightsignal V_(AMB), and, thereupon, to the controller 40. Each of the AGC26, low-pass filter 28, and the amplifier 30 has a control inputconnected to control lines 32, 34, 36, which can be adjusted undercontrol of the controller 40. The controller 40 can measure theamplitude of the received ambient light signal V_(AMB), and compare thatamplitude to the threshold.

In addition, the controller 40 can detect the ambient light signalV_(AmB) by executing a fast Fourier transform (FFT) on the outputsignals on the first and second channels. Assuming that the gains on thefirst and second channels are kept substantially constant, the FFTsignal processing will result in a first set of peaks at a firstfrequency on the first and second channels, and a second set of peaks ata second frequency on the first and second channels. The controller 40can then compare each set of peaks at each frequency. If the peaks areunequal in magnitude, then this indicates that the information signalV_(ABP) is present. If the peaks are about equal in magnitude, then thisindicates that the ambient signal V_(AMB) is present. Once the magnitudeof the ambient signal V_(AMB) is known, then the controller 40 can actto suppress it.

In FIG. 2, the presence of the ambient light signal V_(AMB) is tolerateddue to its low measurement or magnitude, i.e., below the threshold.However, in FIG. 3, the presence of the ambient light signal V_(AMB)cannot be tolerated due to its high measurement or magnitude, i.e.,equal to or above the threshold, which is why the suppression circuit140 is employed to remove the ambient light signal V_(AMB). Thesuppression circuit 140 in FIG. 3 is configured as a correlated doublesampling (CDS) circuit having a pair of switches S1 and S2 which arepulsed out of phase with respect to each other. To use the CDS circuit140, the controller 40 must pulse or modulate the laser light source 46with the laser drive circuit 108 via the control line 110 so that amodulated current I_(MOD) is conducted to the laser light source 46. Thelaser light source 46 is pulsed at a rate or frequency sufficiently fastto accurately resolve the narrowest bar or space used in the type of barcode symbol 70 to be read. Typically, this amounts to several pulsesduring the period of time required for the scanning laser beam to scanacross the narrowest bar or space of the bar code symbol 70.

As also shown in FIG. 3, the signal processing receiver circuit alsoincludes an oscillator 130 that is controlled by the controller 40 via acontrol line 132. The oscillator 130 puts out a clock signal (CLK) whichhas the same frequency as that of the pulsed laser light source 46. Aninverter 134 puts out an inverted clock signal (CLK*) which has the samefrequency as the CLK signal, but which is 180 degrees out of phasetherewith. The CLK* signal drives the switching of the switch S1, andthe CLK signal drives the switching of the switch S2.

In FIG. 3, the first photodetector PD1 outputs a combined output signal(V_(ABP (MOD))+V_(AMB)) that is the sum of the modulated informationsignal V_(ABP (MOD)) and the ambient light signal VA m. This combinedoutput signal is conducted to each switch S1 and S2. When the switch S2is closed, the laser light source 46 is modulated high so that thecombined output signal (V_(ABP(MOD))+V_(AMB)) passes through the switchS2 and is stored on capacitor C2. When the switch S1 is closed, thelaser light source 46 is modulated low so that only the ambient lightsignal V_(AMB) of the combined output signal (V_(ABP (MOD))+V_(AMB))passes through the switch S1 (V_(ABP(MOD))=0) and is stored on capacitorC1. The resulting stored signals are then buffered by buffers B1 or B2and fed into a differencing amplifier 136 (AMP3), which receives the twobuffered signals and subtracts the value of the combined output signal(V_(ABP(MOD))+V_(AMB)) from the value of the ambient light signalV_(AMB), thereby resulting in just the modulated information signalV_(ABP(MOD)), which is then passed through a low-pass filter 138. Theswitching action of the switch S2 is synchronized with the pulsing ofthe laser light source 46, and functions as a demodulator, and moves themodulated information signal V_(ABP(MOD)) to baseband, thereby resultingin the information signal V_(ABP), which is then conducted through theback-end section 120, the digitizer 124, and the decoder 128, asdescribed above. The filter 138 has an adjustable cutoff frequency inits bandwidth (BW1) that is adjusted by the controller 40 via a controlline 142. The filter 138 removes any carrier-related residue.

The suppression circuit 140 effectively suppresses the ambient lightsignal, but incurs a noise performance penalty, because receiverbandwidths need to be increased to support the high modulation frequencycarrier. During demodulation in the suppression circuit 140, the noisein baseband is significantly increased. Also, about half of the outputpower of the laser light source 46 is lost during the modulation (50%duty cycle) to produce the carrier. To avoid this signal-to-noise (S/N)loss (and loss in reader performance), various adjustments can be madeto the signal processing circuit. For example, the gain of the amplifierAMP1 over control line 104 can be increased to improve thesignal-to-noise performance. The clock frequency of the oscillator 130can be lowered over control line 132 to improve fidelity and thesignal-to-noise performance. The cutoff frequencies of the filtershaving bandwidths BW1, BW2 can be adjusted over control lines 142, 118(the lower the bandwidth BW1, BW2, the lower the noise).

FIG. 4 shows another embodiment of a noise suppression circuit 150. Likereference numerals have been used in FIG. 4 to identify like parts.Rather than using correlated double sampling as described above in FIG.3, the received information signal is amplitude modulated by modulatingthe laser light source 46. The combined output signal(V_(ABP(MOD))+V_(AMB)) is conducted to a band-pass filter 152, whichremoves the interference signal V_(AMB). The band-pass filter 152 has anadjustable bandwidth that is adjusted by the controller 40 via a controlline 156. A mixer (M) 154 is then used to demodulate and move themodulated information signal V_(ABP(MOD)) back to a baseband signalV_(ABP). The baseband signal V_(ABP) is then filtered in the low-passfilter 138, if needed, to remove any carrier-related residue.

As depicted in the flow chart of FIG. 8, beginning a reading session atstart step 200, the ambient light signal from the second photodetectorPD2, in accordance with one embodiment, is measured in step 202. Then,in step 204, it is determined whether the measured ambient light signalexceeds a threshold. If not, then both the information signal and theambient light signal from the first photodetector PD1 are processed instep 206, and the reading session ends at step 208. If yes, then thelaser light source 46 is modulated in step 210. Then, the ambient lightsignal from the first photodetector PD1 is suppressed in step 210. Then,only the information signal from the first photodetector PD1 isprocessed in step 214, after which the reading session ends at step 216.

It will be understood that the default operating mode is as shown inFIG. 2, wherein the front-end receiver section 100 and the back-endreceiver section 120 are utilized to process the output signals of thefirst and second photodetectors. As noted above, the suppressioncircuits 140, 150 add noise. In the case where modulation and a dutycycle are employed, the brightness of the outgoing laser beam isreduced. Hence, the suppression circuits 140, 150 are only madeoperational when they are needed, i.e., when the ambient light level istoo high to be ignored.

In the foregoing specification, specific embodiments have beendescribed. However, one of ordinary skill in the art appreciates thatvarious modifications and changes can be made without departing from thescope of the invention as set forth in the claims below. Accordingly,the specification and figures are to be regarded in an illustrativerather than a restrictive sense, and all such modifications are intendedto be included within the scope of present teachings.

The benefits, advantages, solutions to problems, and any element(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeatures or elements of any or all the claims. The invention is definedsolely by the appended claims including any amendments made during thependency of this application and all equivalents of those claims asissued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual such relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has,”“having,” “includes,” “including,” “contains,” “containing,” or anyother variation thereof, are intended to cover a non-exclusiveinclusion, such that a process, method, article, or apparatus thatcomprises, has, includes, contains a list of elements does not includeonly those elements, but may include other elements not expressly listedor inherent to such process, method, article, or apparatus. An elementproceeded by “comprises . . . a,” “has . . . a,” “includes . . . a,” or“contains . . . a,” does not, without more constraints, preclude theexistence of additional identical elements in the process, method,article, or apparatus that comprises, has, includes, or contains theelement. The terms “a” and “an” are defined as one or more unlessexplicitly stated otherwise herein. The terms “substantially,”“essentially,” “approximately,” “about,” or any other version thereof,are defined as being close to as understood by one of ordinary skill inthe art, and in one non-limiting embodiment the term is defined to bewithin 10%, in another embodiment within 5%, in another embodimentwithin 1%, and in another embodiment within 0.5%. The term “coupled” asused herein is defined as connected, although not necessarily directlyand not necessarily mechanically. A device or structure that is“configured” in a certain way is configured in at least that way, butmay also be configured in ways that are not listed.

It will be appreciated that some embodiments may be comprised of one ormore generic or specialized processors (or “processing devices”) such asmicroprocessors, digital signal processors, customized processors, andfield programmable gate arrays (FPGAs), and unique stored programinstructions (including both software and firmware) that control the oneor more processors to implement, in conjunction with certainnon-processor circuits, some, most, or all of the functions of themethod and/or apparatus described herein. Alternatively, some or allfunctions could be implemented by a state machine that has no storedprogram instructions, or in one or more application specific integratedcircuits (ASICs), in which each function or some combinations of certainof the functions are implemented as custom logic. Of course, acombination of the two approaches could be used.

Moreover, an embodiment can be implemented as a computer-readablestorage medium having computer readable code stored thereon forprogramming a computer (e.g., comprising a processor) to perform amethod as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, a CD-ROM, an optical storage device, a magnetic storagedevice, a ROM (Read Only Memory), a PROM (Programmable Read OnlyMemory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM(Electrically Erasable Programmable Read Only Memory) and a Flashmemory. Further, it is expected that one of ordinary skill,notwithstanding possibly significant effort and many design choicesmotivated by, for example, available time, current technology, andeconomic considerations, when guided by the concepts and principlesdisclosed herein, will be readily capable of generating such softwareinstructions and programs and ICs with minimal experimentation.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. In addition, in theforegoing Detailed Description, it can be seen that various features aregrouped together in various embodiments for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments require morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus, the following claimsare hereby incorporated into the Detailed Description, with each claimstanding on its own as a separately claimed subject matter.

1. A reader for electro-optically reading a target in the presence ofambient light to be suppressed, comprising: a laser for emitting a laserbeam; a scan component for scanning the laser beam across the target forreflection and scattering therefrom as return laser light; a detectorassembly for detecting the return laser light from the target and forconverting the detected return laser light into an analog electricalinformation signal bearing information related to the target, and forconcomitantly detecting the ambient light and for converting thedetected ambient light into an analog electrical ambient light signal,the detector assembly including a first photodetector having a firstfield of view and a first light collection area, a second photodetectorhaving a second field of view and a second light collection area inclose proximity to the first light collection area, and a detector lensspaced from the first and second photodetectors and operative forfocusing and directing the return laser light substantially onto thefirst light collection area over the first field of view, the firstlight collection area being operative for generating a first analogelectrical output signal comprised of the information signal and theambient light signal, and the second light collection area beingoperative for generating a second analog electrical output signalsubstantially comprised of the ambient light signal; and signalprocessing circuitry for processing the first and second output signalsto determine a magnitude of the ambient light signal, and forsuppressing the ambient light signal when the determined magnitude ofthe ambient light signal at least equals a threshold.
 2. The reader ofclaim 1, wherein the signal processing circuitry includes a controllerfor comparing the ambient light signal from the second photodetectorwith the threshold, the signal processing circuitry being operative forprocessing the first output signal in one mode of operation when theambient light signal from the second photodetector is below thethreshold, and for suppressing the ambient light signal in the firstoutput signal and for processing substantially only the informationsignal in the first output signal in another mode of operation when theambient light signal from the second photodetector at least equals thethreshold.
 3. The reader of claim 2, wherein the signal processingcircuitry includes a correlated double sampling (CDS) circuit forsuppressing the ambient light signal in the first output signal, and acontrol switch having two switching states; and wherein the controlleris operative for switching the control switch to one of the switchingstates in which the CDS circuit is bypassed during the one mode ofoperation, and for switching the control switch to the other of theswitching states in which both the information signal and the ambientlight signal in the first output signal are conducted to the CDS circuitduring the other mode of operation.
 4. The reader of claim 3, whereinthe CDS circuit includes a differential amplifier having one input towhich both the information signal and the ambient light signal areconducted, another input to which the ambient light signal is conducted,and an output from which the ambient light signal has been suppressed.5. The reader of claim 3, wherein the controller is operative formodulating the laser to generate a modulated information signal duringthe other mode of operation, and wherein the CDS circuit includes ademodulator for demodulating the modulated information signal.
 6. Thereader of claim 2, wherein the signal processing circuitry includes abandpass filter for suppressing the ambient light signal in the firstoutput signal, and a control switch having two switching states; andwherein the controller is operative for switching the control switch toone of the switching states in which the bandpass filter is bypassedduring the one mode of operation, and for switching the control switchto the other of the switching states in which both the informationsignal and the ambient light signal in the first output signal areconducted to the bandpass filter during the other mode of operation. 7.The reader of claim 6, wherein the controller is operative formodulating the laser to generate a modulated information signal duringthe other mode of operation, and wherein the signal processing circuitryincludes a mixer for demodulating the modulated information signal. 8.The reader of claim 1, wherein each light collection area is elongated,and wherein the light collection areas lie on a common substrate.
 9. Thereader of claim 8, wherein the second light collection area liesexteriorly of the first light collection area.
 10. A detector assemblyfor detecting return laser light from a target in the presence ofambient light, and for converting the detected return laser light intoan analog electrical information signal bearing information related tothe target, and for concomitantly detecting the ambient light, and forconverting the detected ambient light into an analog electrical ambientlight signal, the detector assembly comprising: a first photodetectorhaving a first field of view and a first light collection area; a secondphotodetector having a second field of view and a second lightcollection area in close proximity to the first light collection area; adetector lens spaced from the first and second photodetectors andoperative for focusing and directing the return laser lightsubstantially onto the first light collection area over the first fieldof view; wherein the first light collection area is operative forgenerating a first analog electrical output signal comprised of theinformation signal and the ambient light signal; and wherein the secondlight collection area is operative for generating a second analogelectrical output signal substantially comprised of the ambient lightsignal.
 11. The detector assembly of claim 10, wherein each lightcollection area is elongated, and wherein the light collection areas lieon a common substrate.
 12. The detector assembly of claim 10, whereinthe second light collection area lies exteriorly of the first lightcollection area.
 13. The detector assembly of claim 10, wherein thesecond light collection area surrounds the first light collection area.14. A method of electro-optically reading a target in the presence ofambient light to be suppressed, comprising: emitting a laser beam from alaser; scanning the laser beam across the target for reflection andscattering therefrom as return laser light; detecting the return laserlight from the target; converting the detected return laser light intoan analog electrical information signal bearing information related tothe target; concomitantly detecting the ambient light; converting thedetected ambient light into an analog electrical ambient light signal;generating a first analog electrical output signal comprised of theinformation signal and the ambient light signal from a firstphotodetector having a first field of view and a first light collectionarea; generating a second analog electrical output signal substantiallycomprised of the ambient light signal from a second photodetector havinga second field of view and a second light collection area in closeproximity to the first light collection area; focusing and directing thereturn laser light substantially onto the first light collection areaover the first field of view; processing the first and second outputsignals to determine a magnitude of the ambient light signal; andsuppressing the ambient light signal when the determined magnitude ofthe ambient light signal at least equals a threshold.
 15. The method ofclaim 14, wherein the suppressing of the ambient light signal isperformed by comparing the ambient light signal from the secondphotodetector with the threshold, by processing the first output signalin one mode of operation when the ambient light signal from the secondphotodetector is below the threshold, by suppressing the ambient lightsignal in the first output signal, and by processing substantially onlythe information signal in the first output signal in another mode ofoperation when the ambient light signal from the second photodetector atleast equals the threshold.
 16. The method of claim 15, wherein thesuppressing of the ambient light signal is performed by conducting boththe information signal and the ambient light signal in the first outputsignal to a correlated double sampling (CDS) circuit.
 17. The method ofclaim 16, and modulating the laser to generate a modulated informationsignal during operation of the CDS circuit, and demodulating themodulated information signal during operation of the CDS circuit. 18.The method of claim 15, wherein the suppressing of the ambient lightsignal is performed by conducting both the information signal and theambient light signal in the first output signal to a bandpass filter.19. The method of claim 18, and modulating the laser to generate amodulated information signal during operation of the bandpass filter,and demodulating the modulated information signal during operation ofthe bandpass filter.
 20. The method of claim 15, and elongating eachlight collection area, configuring the light collection areas to lie ona common substrate, and configuring the second light collection area tolie exteriorly of the first light collection area.